Session J2: Molecular Spectroscopy

Raman Spectroscopy of Plants

Raman spectroscopy has been used for fast, noninvasive tool for chemical analysis of complex biological systems such as plants. Application of lasers to plant identification and taxonomy offers advantages over traditional methods. Raman spectra provide spectroscopic signatures of plant chemical composition. New applications of portable and lab-based Raman spectroscopy and microscopy of plants will be presented. Advantages and limitations of current instruments will be discussed.   

Laser-Induced Breakdown Spectroscopy of Plant Materials

Plant stress can be caused by many factors including drought, pollution, and microbial infestations; to name a few. Because many of these issues can affect agricultural crop yield, we use focused femtosecond laser pulses to perform laser-induced breakdown spectroscopy (LIBS) on plant materials in order to detect the effects of stress on plant life. LIBS has the advantage of being simple in its set-up making it an ideal candidate for performing plant stress detection in the field.   

Raman Confocal Microscopy and its application on plant samples

We introduce our new Lab Ram-HR evolution Confocal Raman Microscope. We also discuss its application to the plant samples. It is including to record Raman spectra, to suppress some fluorescence, and to take Raman imaging.   

Raman Spectroscopy and Imaging of Red Blood Cells

Raman spectroscopy is a powerful spectroscopic technique that can be used for vibrational imaging of biological systems. We demonstrate Raman spectra and images of red blood cells (RBC) and ``ghost cells'' with hemoglobin removed and replaced with other molecules. We investigate the dependence on various experimental parameters such as different laser wavelengths and intensities. Our preliminarily results confirm the detection of hemoglobin in RBC and have a potential for future applications in nanoscale cell surface imaging.   

TERS and AFM Mapping of Molecular Aggregates

Tip-enhanced Raman spectroscopy is a well-known analysis technique for surfaces and other material science. We combined TERS mapping with a simultaneous AFM mapping in order to correlate topographical features with corresponding Raman spectra. We applied this technique to image copper phthalocyanine molecular aggregates on a molybdenum disulfide substrate. Our results showed chemically-enhanced Raman ``hot spots'' on the sample surface. These did not correspond with the Raman hot spots observed without the tip. This is the first imaging of chemically-enhanced Raman hot spots on a semiconductor surface.   

Tip-Enhanced Raman Spectroscopy of Functionalized Nanoparticles

Raman spectroscopy has been widely used for analyzing a wide range of materials. Tip-enhanced Raman spectroscopy (TERS) is one of the advanced strategies used to provide high spatial resolution and enhanced Raman signals simultaneously. TERS enhances Raman signals significantly for molecules located in the gap between plasmonic metal nanoparticles. This enhancement is attributed to the increase of electromagnetic field strength in the gap. However, some studies also show remarkable enhancements of Raman signals from molecules outside of the gap. We investigate the underlying mechanisms of TERS using nanoantenna formed by functionalized nanoparticles and nano tips. The results may be applied to studying bio-molecular interactions, which are essential for understanding the biological processes in living cells.   

Coherent Surface-Enhanced Resonant Raman Spectroscopy

Spontaneous Raman scattering has been widely used to perform molecular chemical analysis but weak signals from small amounts of material present a challenge. Surface-enhanced Raman scattering (SERS) and coherent anti-stoke Raman scattering (CARS) spectroscopies are two of the most common techniques to enhance the Raman signals. Several attempts have been done to combine those techniques to reach the maximum signal enhancement. We investigate resonant Raman effects for enhanced Raman scattering and combine it with surface and coherence enhancements.   

Resolving Spectral Congestion in Time-Resolved Surface-Enhanced Coherent Raman Signals using Compressed Sensing

Experimental noise often limits spectral and temporal resolution in coherent nonlinear optical spectroscopy. For example, in time-resolved surface-enhanced coherent anti-stokes Raman scattering (SECARS) spectroscopy the spectral resolution increases with a decreasing size of the pulse shaper slit but the signal-to-noise ratio decreases [1-3]. The theoretical limits of resolution in time-resolved CARS have previously been discussed [4]. We apply the compressed sensing (CS) technique to improve data analysis and to reach the theoretical spectral resolution in noisy SECARS signals.   

Coherent anti-Stokes Raman scattering with a single broadband pulse

Here we demonstrate single-beam coherent anti-Stokes Raman scattering (CARS) with a spectral notch consisting of a narrow wire placed in a 4-f pulse shaper. This was previously done by using resonant photonic crystal slab. Our current setup can be used in both forward detection and epi-detection, and is promising in achieving low-wavenumber Raman shift (\textless\ 200 cm$^{-1})$ measurements.   

Ultrashort Pulse Microscopy for Three-Dimensional, \textit{In-Vivo} Biological Imaging

As laser technology continues to advance, optical imaging is becoming more prevalent in biological applications. Commonly used methods, such as confocal microscopy, offer high resolution and three-dimensional imaging capabilities, but often harm the sample. Thus, there is a need for methods that offer such advantages while doing no harm. Ultrashort Pulse Microscopy (UPM), an optical imaging method utilizing sub 10-fs laser pulses, may be the solution to this problem. UPM offers the ability to obtain multimodal, three-dimensional in-vivo images of a biological sample. In this talk, we will discuss the relevant theory, instrumentation and implementation of our UPM system.